Bill writes:
Thank you for your inquiry. The difference between an ACOG designed for the M16A4 (20” barrel) versus an ACOG designed for the M4 (14.5” barrel) is in the bullet drop compensator (BDC) portion of the reticle. The M16A4 BDC is calibrated for M855 with a muzzle velocity of 3100 fps. The M4 BDC is calibrated for 2900 fps. The one combination that can cause unacceptable accuracy is putting an ACOG designed for a 20” barrel on a weapon with a 14.5” barrel.
The USMC TA31RCO-A4 is calibrated for a 20” barrel.
The USMC TA31RCO-M4 and Army TA31RCO-M150 are calibrated for a 14.5” barrel.
_________________ ArmyProperty.com Team
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